Reducing IGBT losses in ZCS series resonant converters

The fundamental operational parameter that controls the losses in series resonant converters was found to be the (reflected) DC voltage transfer ratio. Losses which are a function of the average current (such as conduction losses of IGBTs and diodes) are independent of the switching frequency. Losses which are associated with the rms current are a function of both the (reflected) DC voltage ratio and the switching frequency ratio. Universal and normalized graphs, derived in this study, can be conveniently used to assess the expected rms and average current conduction losses under any given operational conditions. The residual switching losses in `ZCS' series resonant converters operating in Continuous Current Mode, can be reduced by simple current snubbers placed in the commutation circuits. The experimental results of this study confirm the theoretical predictions and demonstrate that the turn on snubbers can reduce switching losses by about 1.5% at a switching frequency of 65 kHz.